For an optimal thermal performance, a lighting device comprises a heat sink equipped with fins, for example back-reflecting lamp bulbs of type PAR, MR, BR, GU, etc. “PAR” means parabolic aluminized reflector. “MR” means multifaceted reflector. “BR” means bulged reflector, and “GU” refers to a U-shaped lamp with a plug-in lamp base. The light sources of the lamps include conventional halogen filaments or LED light sources.
Conventional heat sinks are made of die cast metal, such as aluminum, with high manufacturing and raw material costs. Further, for aesthetic reasons, a non-technical appearance without a visible cooling structure is desired. If the heat sink structure is hidden behind a smooth outer surface, airflow through the cooling structure is preferred for improved thermal performance, which requires inlet and outlet openings. For the desired look-and-feel, these openings should be small. However, a small channel has a high airflow resistance, reducing the cooling performance of the heat sink structure. Since the cooling performance is mainly determined by the amount of air that flows through the cooling structure, also referred to as internal channel, this will reduce the cooling performance of the heat sink.
US2012/0044680A1 discloses an illustrator with LED including a rear housing having a cavity. A front housing is disposed in the cavity, wherein the front housing includes through holes. An illuminating module is sandwiched between the rear housing and the front housing. Air holes are formed on the sidewall of the rear housing, so that the cavity can communicate with outside air.
An example of a retrofit lamp with a smooth outer appearance may be found in the patent application PCT/IB2013/052999 “Lighting Device with Smooth Outer Appearance”, incorporated herein by reference. As shown in FIG. 1, the retrofit lamp 100′ comprises at least one light source 101′; a heat sink component 104′, having a bottom 1043′ and a sidewall 1044′ extending from the bottom 1043′, wherein the bottom 1043′ comprises a concave part 1041′ and wherein the at least one light source 101′ thermally contacts the concave part 1041′ of the heat sink component 104′; and a cover 103′ provided on the sidewall 1044′ opposite to the bottom 1043′, thereby defining an air chamber 1051′ between the cover 103′, the sidewall 1044′, the bottom 1043′ and the concave part 1041′. The heat sink component 104′ comprises a cover opening 102′ and a heat sink opening 106′. The air chamber 1051′ forms a channel between the cover opening and the heat sink opening to allow a flow of air 105′ between the cover opening and the heat sink opening or vice versa. A housing 107′ is provided between the heat sink component 104′ and the base 109′. A driver assembly 108′ is provided between the housing 107′ and the concave part 1041′. When the lamp 100′ is mounted in a vertical operating position as shown in FIG. 2, the air surrounding the lamp warms up during lamp operation, and the warm air will rise because of natural convection.
While the thermal rating, i.e. the maximum temperature for which they are rated to operate without being negatively affected, of most of the components of both the driver assembly and the light source is above 125° C., some of them, such as the electrolytic capacitor(s), are more sensitive to high temperatures. However, the construction of the previous types of lamps results in an unsuitable arrangement, as the thermally sensitive components on the driver assembly 108′ are heated by the rising warm air.
It is desired to combine optimal heat dissipation with the advantages of a smooth outer appearance of the lighting device.